Method for producing titanium strip



United States Patent 3,420,172 METHOD FOR PRODUCING TITANIUM STRIPAdrian Burt Sauvageot, Toronto, and James M. Partridge,

Steuhenville, Ohio, assignors to Titanium Metals Corporation of America,New York, N.Y. No Drawing. Filed Nov. 9, 1966, Ser. No. 592,995 Int. Cl.C22f 1/18, 1/16 US. Cl. 148-115 25 Claims ABSTRACT OF THE DKSCLOSUREMethod for producing strip having a substantially recrystallizedmicrostructure from commercially pure titanium, alpha, stabilized alphatype titanium base alloys, and alpha stabilized alphabeta type titaniumbase alloys comprising unidirectionally hot rolling a metal body from atemperature requiring a substantial amount of reduction in thealpha-beta field, heating said rolled metal at a temperature above thebeta transus of said metal to transform the crystal structure of saidmetal to the beta phase and rapidly cooling said metal to a temperaturebelow the beta phase to produce an acicular type microstructure in themetal followed by rolling and annealing said metal at temperatures belowthe beta transus.

This invention relates to a method for the manufacture of titanium andtitanium alloy strip which is particularly characterized by freedom fromthe tendency to either rib or ridge, good ductility and minimumanisotropy of mechanical properties. More particularly, the method ofour invention permits the production of equiaxed substantiallycompletely recrystallized elongated strip which may be rolled to finishgauge or fabricated. Our method may be successfully applied tocommercially pure titanium and to alpha and alpha-beta type titaniumalloys containing alpha stabilizers.

Ribbing and ridging are indicated by longitudinal striations which occurin titanium metal which has been unidirectionally rolled at temperatureshigh in the alphabeta field and which are oriented in the direction ofrolling, Ribbing refers to the striations which develop duringsubsequent rolling of the strip to finish gauge, and ridging refers tothe striations which develop during testing of rolled strip or duringfabrication of products therefrom. Both of these effects are believed tobe caused by crystallographic orientations imparted to the metal duringthe unidirectional rolling of bars and billets into a hot band.Anisotropy is also created in the metal by unidirectional rolling and isevidenced by a difference between the mechanical properties of the stripwhen measured parallel to the direction of rolling and when measuredtransversely of the direction of rolling.

Since ribbing and ridging in titanium and titanium base alloys areapparently created by unidirectional rolling of the metal in or throughthe two-phase alpha-beta field, they could be avoided by rolling attemperatures sufiiciently low to avoid deformation in the alpha-betafield. Additionally, ribbing, ridging and anisotropy of mechanicalproperties may be eliminated by cross rolling the metal body at rightangles to the original direction of rolling to an extent to obtainapproximately the same degree of reduction as obtained during theoriginal rolling. However, low temperature rolling is not practical withtitanium alloys since suflicient reduction cannot be obtained and crossrolling is not practical for the commercial production of eithertitanium or titanium alloy strip.

Initial rolling at temperatures in the beta field or relatively high inthe alpha-beta field is essential for the production of a hot band ofalpha and alpha-beta type titanium alloys for subsequent rolling tofinish strip since reduction of a billet or bar to a hot band involves asubstantial decrease in size. This reduction must be initiated atelevated temperatures since the alloys have a low specific heat and aconsequent rapid temperature drop, and it is important that the metal besufficiently plastic to per mit rapid and easy deformation. Although anelevated temperature is essential for easy deformation, the temperatureshould not be so high as to cause excessive oxidation and scaling of themetal surface during deformation. Practical temperatures from thestandpoint of ease of deformation and avoidance of excessivecontamination of the metal surface are high in the alphabeta field orlow in the beta field; and substantial reduction at other temperaturesis not practical.

Although cross rolling will eliminate ribbing and ridging and willsubstantially decrease directionality, cross rolling is limited to sheetproducts having a length not much greater than their width since thedimensions of the sheet must be such that it can pass crosswise throughthe rolling mill. Since cross rolling is of necessity limited to sheetshaving a length no greater than the roll width, it obviously cannot beapplied to elongated hot bands having lengths of a hundred feet or morewhich are to be rolled into even longer strips.

Heat treatment of commercially pure titanium and alpha and alpha-betatype titanium alloys by annealing at a temperature near the beta transusof the metal prior to reduction to eliminate ribbing and ridging and todecrease anisotropy is disclosed in United States Patent No. 3,169,085.While the method disclosed in this patent will reduce the tendencytoward ribbing and ridging and will reduce anisotropy, the resultingmicrostructure of commerically pure titanium and alpha and alpha-betatype alloys processed in accordance with the method is such thatductility is extremely poor; and, therefore, the metal cannot be furtherreduced or fabricated without catastrophic internal shear cracking ofthe metal. The extent of the shear cracking has been found to bedependent upon the annealing temperature and the rate of cooling fromthe annealing temperature. In order to produce a strip which will nothave a tendency to rib or to ridge and which can be successfully rolledand fabricated, we have found it essential that the strip be annealed ata temperature above the beta transus of the metal and that the strip berapidly cooled to a temperature below the beta transus. Treatment inthis manner creates a substantially completely acicular typemicrostructure in the metal as opposed to the lamellar or to theWidmanstatten type structure which is created when the metal is cooledat a slower rate. Rapid cooling in accordance with our invention may beobtained by immersion, spraying or extremely fast air cooling; and themethod of cooling will depend upon the specific material and thethickness of the strip being processed. Annealing at a temperature abovethe beta transus and rapid cooling to a temperature below the betatransus are termed a beta quench hereinafter.

Summarized briefly, our invention provides a method for producing stripof commercially pure titanium and alpha and alpha-beta type titaniumalloys containing alpha stabilizers which is characterized by freedomfrom ribbing and ridging, minimum anisotropy of mechanical propertiesand good ductility. Strip produced according to our invention can becold rolled to finish gauge and fabricated without failure due tointernal shear cracking. Basically, our method comprisesunidirectionally hot rolling the metal from a temperature in its betafield or high in its alpha-beta field; heating the rolled metal to atemperature above its beta transus and rapidly cooling to a temperaturebelow the beta transus to create a substantially completely acicularmicrostructure and subsequently deforming and annealing the metal tosubstantially completely recrystallize the microstructure. The betaquench may be performed on the hot band immediately after theunidirectional rolling, or it may be performed later in the processafter the hot band has been reduced. After the beta quench, it isnecessary that the metal be subjected to deformation and annealing in amanner and to an extent to effect substantially completerecrystallization of the microstructure in the metal. It is essentialthat the microstructure be substantially completely recrystallized forthe metal to have sufiicient ductility to permit subsequent cold rollingand fabrication Without failing due to internal shear cracking. The termcold rolling as used herein encompasses rolling between about roomtemperature and about 300 F.

Metal which may be advantageously treated by the method of our inventionis selected from the group consisting of commercially pure titanium,alpha type titanium alloys and alpha-beta type titanium alloys. Thealloys must be alpha stabilized since beta stabilized alpha-beta alloysare susceptible to the formation of the brittle omega phase during rapidcooling from the beta field. Commercially pure titanium is available invarious grades depending upon hardness, and the compositions of thegrades differ principally in the content of the interstitials, oxygen,nitrogen and carbon. Generally speaking, commercially pure titanium hasalpha type microstructure at room temperature and will convert to thebeta crystal form at temperatures above its beta transus. Alpha typetitanium alloys have an alpha microstructure at room temperature andcontain alpha stabilizers of which aluminum, tin and columbium areexamples. An alloy containing 5% aluminum, 2.5% tin, balance titanium,is typical of the alpha type alloys. The alpha-beta type titanium alloyshave a mixture of alpha type microstructure and beta type microstructureat room temperature and are exemplified by an alloy containing 6%aluminum, 4% vanadium, balance titanium. A group of alloys generallydesignated alpha lean beta type contain a substantial amount of alphastabilizing agent and a minor proportion of beta stabilizing agent andare subject to treatment by our method since the alpha stabilizerpredominate. An alloy containing 8% aluminum, 1% vanadium, 1%molybdenum, balance titanium is a typical alpha lean beta type.

The initial hot rolling step to reduce the bar, billet or other shape tohot band is initiated at a temperature in the beta field or high in thealpha-beta field of the metal being processed. Any type of rolling millmay be employed, and the dimensions of the starting shape are notmaterial so long as the shape will fit into the mill. Conveniently, theinitial rolling is carried out by heating the metal body to the startingtemperature heat or above the beta transus and then passing it throughthe rolling mill, rolling being continued as the temperature of themetal drops. A large portion of the reduction and certainly the laterpart thereof is accomplished in the alpha-beta field of the metal beingrolled due to the low specific heat of titanium and titanium basealloys.

After rolling, the metal is heated to a temperature above its betatransus. This is accomplished in any suitable manner by conventionalapparatus and may be carried out by placing a coil in a furnace althoughit is preferable to continuously heat successive portions of a hot bandor strip. Maintenance of titanium and titanium base alloys at atemperature above the beta transus for an extended period of time isundesirable because it coarsens the grain structure; and, if the heatingis carried out without the protection of an inert atmosphere, surfaceoxidation and scaling occur. It is, however, essential that the metal beheld above the beta transus for a suflicient time to in- I sure completetransformation of the entire metal body to beta structure; and,therefore, the duration of the anneal will depend upon the temperatureof the heating furnace and the size and shape of the body being heated.For example, in the case of a closely wound coil, sufiicient time mustbe allowed for the innermost convolutions to be raised to temperature.When a continuous anneal is utilized to raise successive portions of hotband or strip to temperature the time required at temperature will bevery short since the hot band or strip will be rapidly heatedthroughout. The precise temperature employed for the anneal is notcritical providing it is above the beta transus of the metal beingtreated. A preferred maximum is about F. above the beta transus sincethis provides a margin of safety insuring complete heating above thebeta transus and is not so high as to coarsen the grain size and produceexcessive surface oxidation and scaling.

After the metal has been completely transformed to beta structure, it israpidly cooled to produce the required substantially completely acicularmicrostructure for subsequent recrystallization. Rapid cooling of themetal to a temperature below the beta transus is absolutely essentialfor the success of our process as it is not possible to obtainrecrystallization by subsequent deformation and annealing unless themetal is beta quenched to create the acicular microstructure necessaryfor recrystallization. As will be shown hereinafter, the ductility ofunrecrystallized strip as determined by bend tests is low. Cooling maybe accomplished by either immersion or spraying, and any coolant whichwill rapidly decrease the temperature of the metal may be used.Additionally, air cooling is suflicient to rapidly lower the temperatureof very thin strip. As stated heretofore, the beta quench may beperformed immediately after hot rolling, or it may be carried out as anintermediate step between reductions.

The precise temperature at which the microstructure will becomesubstantiallycompletely acicular in the rapidly cooled or beta quenchedmetal will vary depending largely on the particular composition of themetal, as will be appreciated by those skilled in the art. However, inall instances, this temperature will be lower than the beta transus ofthe metal. For practical application of the method, it is preferable tocool the heated metal to room temperature since the formation of thenecessary acicular microstructure is insured and a minimum of control isrequired. However, it is not essential that the metal be cooled to roomtemperature; and if control conditions permit, it may be cooled to atemperature above room temperature. In addition to cooling the metal toa temperature below 1ts beta transus, it is necessary that the rate ofcooling be rapid to produce acicular microstructure in the metal. ThlSmicrostructure will be readily recognized by those skilled in the art bythe appearance of a section of the metal cut, polished and etched byconventional techniques and examined under a microscope. Themicrostructure consists principally of needle-like grains more or lessrandomly oriented. The aciculas may have more than three habit planes,that is, they may be oriented or grouped in more than three directions.Such a microstructure is readily distinguishable from that obtained byslower cooling from the beta field which will consist principally ofplatelet alpha titanium in basketweave or Widmanstatten array. Usuallythe platelets will lie in no more than three directions in blockssmaller than the original beta grains. The acicular microstructure,formed by the rapid cooling from the beta field according to ourinvention, is readily broken up and recrystallized by subsequentdeformation and annealing; and this substantially completelyrecrystallized microstructure provides good ductility in the finalstrip.

After the beta quench, the metal is treated by a sequence of rolling andannealing steps designed to create recrystallized microstructure in themetal. The deformation of the metal during rolling imparts strain to themetal, and subsequent annealing tends to relieve the strain andrecrystallizes the grain structure. Partial stress relief is obtained byintermediate anneals, and the final anneal results in complete stressrelief and substantially complete recrystallization. As would beexpected, the precise sequence of rolling and annealing applied to thebeta quenched metal and the temperature of these steps will vary withthe material and thickness being treated, the desired finish gauge ofthe strip and the equipment available. For certain materials a stressrelief anneal is beneficial prior to any deformation immediately afterthe beta quench. Generally speaking, smaller reductions and longerintermediate anneals must be used with lower rolling temperatures toprevent internal shear cracking while larger reductions are required athigher rolling temperatures to impart the required strain to the metalfor subsequent recrystallization.

It is possible to roll some titanium strip products, such ascommercially pure titanium and an alloy containing aluminum, 2.5% tin,balance titanium, at temperatures which permit recrystallizationsimultaneous with rolling. The rolling temperature for simultaneousrecrystallization will be between about 1000 F. and 1200 F. for betaquenched commercial pure titanium and between about 1200 F. and 1400 F.for the alloy containing 5% aluminum, 2.5% tin, balance titanium. Whenrecrystallization occurs during rolling, the final anneal will result instress relief and grain growth and the resulting microstructure, whichis substantially completely recrystallized, is large grained and lessequiaxed than metal which is recrystallized by a final anneal only. Dueto the grain size and orientation in metal which has partiallyrecrystallized during rolling, the metal is less susceptible to furthercold rolling than metal which is recrystallized by a final anneal.However, if no further reduction of the strip is required, rolling attemperatures which permit recrystallization is satisfactory as the stripproduced has no tendency to rib or ridge, has low anisotropy and highductility. For this reason, rolling temperatures for commercially puretitanium and the titanium alloy containing 5% aluminum and 2.5% tinshould be based in part on the work to be done on the material after therolling recrystallization cycle.

It is necessary that the rolling and annealing temperatures be keptbelow the beta transus of the metal since reheating to above the betatransus will require subsequent rapid cooling followed by rollingannealing to obtain the recrystallized structure. It has been found thattemperatures ranging from room temperature to about 1600 F. areacceptable for deforming the beta quenched metal de pending upon themetal and amount of reduction taken in each rolling cycle. Annealingtemperatures from about 1400 F. to about 1700 F. are acceptable, and theprethickness. The temperature decreased during rolling to a finishtemperature of 1650 F., and a majority of the rolling was carried out inthe alpha-beta field. A test panel was cut from the hot band and heatedat a temperature of 1950 F. for three minutes. The panel was thenquenched by rapid immersion in a cold water bath. The beta quenchproduced an acicular type microstructure in the metal.

The beta quenched panel was then subjected to five 15% reduction rollingcycles at room temperature. The panel was line annealed for five minutesat 1 600 F. followed by air cooling after each rolling cycle. The finalanneal effected substantially complete recrystallization, and thefinished cold rolled strip was free from internal cracking and showed noridging when a 2-inch by 10-inch test piece was cold stretched to anelongation of about 10%. No ribbing was discernible either in the finalproduct or at any stage after the beta quench. A specimen of thefinished cold rolled strip was sectioned and polished and itsmicrostructure found to be fine-grained and substantially completelyrecrystallized.

Another bar of Ti-5Al-2.5Sn alloy was unidirectionally hot rolled to0.130 inch thickness from a temperature in the beta field with amajority of the reduction taking place in the alpha-beta field. A panelfrom the hot band was then heated at 1950 F. for five minutes and waterquenched. The beta quenched panel was sandblasted and pickled and rolledat 1000 F. to effect a reduction to 0.051 inch. The test piece was againsandblasted and pickled and was then annealed for ten minutes at 1650 F.and air cooled. No ribbing occurred during the rolling at 1000 F.; and,as indicated in Table A, the mechanical properties of the resultingstrip were good. The microstructure was found to be completelyrecrystallized after the final anneal.

Three other panels from this hot band were processed in the same way andthen subjected to one, two and three 20% reduction cold rolling cycles.Each cold rolling cycle was followed by an anneal at 1600 F. for aperiod of three to five minutes and air cooling. No ridging occurredwhen specimens were stretched to an elongation of at least 10%. Thematerial did not rib during cold rolling, and good mechanical propertiesand low anisotropy were obtained as indicated in Table A. All bends inTable A and in the other tables appearing hereinafter were rated at 20Xmagnification with no observable rupture.

TABLE A Test E, 20X gauge Ftu, Fty, Percent p.s.i. MBR Cold rolling inchDir. K s.i. K s.i. E? X 10 R/T None 051 L 139. 3 125. 0 20. 0 16.3 3. 1T 134. 3 128. 2 21. 0 17. 6 3. 1 One 20% cycle .040 L 134.1 118. 4 20. 016.5 3. 8 T 134. 4 124. 3 20. 2 17.2 3. 1 Two 20% cycles.... 030 L 134.8 122.1 17. 0 16. 3 3. 0 T 133. 3 123. 3 19. 5 17. 7 2'. 6 Three 20%cycles .024 L 137. 7 125. 4 17.0 16. 9 3. 6 T 136. 2 123. 7 19.2 17. 32. 7

*One inch gauge.

cise temperature will be selected in accordance with the metal and thetype of anneal utilized. The duration of the anneal will also vary withthe metal being treated and the annealing temperature. Line annealsranging from five to ten minutes have been used, and box anneals varyingfrom sixteen to forty-eight hours have also been used.

The following non-limiting examples illustrate specific embodiments ofour process as applied to commercially pure titanium and to therepresentative titanium alloys, Ti-5Al-2.5Sn; Ti-6Al-4V andTi-8Al-1Mo-1V.

EXAMPLE I A sheet bar of an alloy containing 5% aluminum, 2.5% tin,balance titanium having a beta transus of 1900 F. :t25 wasunidirectionally hot rolled from a temperature The maximum acceptablebend radius for Ti-5A1-2.5Sn is 4.0 for .070 inch gauge and below and itis apparent that all specimens met this specification.

An additional bar of Ti-5A1-2.5Sn alloy was unidirectionally hot rolledto 0.149 inch thickness from a temperature in the beta field with themajority of the reduction taking place in the alpha-beta field. Twopanels from the hot band were then heated at 1950 F. for five minutesand water quenched. Both beta quenched panels were then rolled to 0.057inch, a total reduction of 60%. One panel was rolled at 1400 F. and theother at 1600 F. No ribbing occurred during rolling and themicrostructure of each panel showed complete recrystallization duringrolling. Mechanical testing after line annealing for ten minutes at 1650F. and air cooling showed low anisotropy, high tensile and bendductility as indicated in of about 2100 F. to produce a hot band of0.135 inch Table B. No ridging occurred after 10% elongation.

7 8 TABLE B A third bar of this alloy was unidirectionally hot rolled20X from a temperature in the beta field to a thickness of 0.175 RollingFtu Fty Percent E, p.s.l. MBR inch. Two panels were cut from the hotband and heated temp-I 131* X 108 R/T for five minutes at 1950 F.followed by water quenching. 1,400 L 124.3 111.9 20.2 16.6 3.5 The betaquenched panels were sandblasted and pickled 1 600 133% igg to removecontamination. The panels were then rolled T 121.5 114.5 19.2 17.2 3.5at 1400 F. and 1600 F. to 0.065 inch, a 60% reduction. inch gauge Eachpanel was annealed at 1450 F. for forty-eight hours i followed by vacuumcooling and pickling. The final micro- EXAMPLE H structure of the panelswas essentially completely recry- A sheet bar of an alloy containing 6%aluminum, 4% stallized. Mechanical tests showed low anisotropy andvanadium, balance titanium having a beta transus of good tensile andbend ductility as indicated in Table D. 1820 F. i25 was unidirectionallyhot rolled from a No ridging occurred on specimens pulled to 10%elontemperature of 1900 F. to produce a hot band of 0.140 gation. inchthickness. The rolling finished at 1500 F.; and, TABLE D therefore, amajor portion of the reduction was accom- 0X plished in the alpha-betafield. A panel from the hot band Rolling Fm Fty Percent E, MBR washeated to a temperature of 1925 F. for five minutes temp, F. D11. Ks.i.Ks.i. El X 10 and then rapidly quenched by immersion in water. The 1,400130,3 114 4 ltaletanigzpch produced an acicular type microstructure in1,6O0 g 35 9 55 g g igg 5:? e

' EXAMPLE III Roll-157 reduction Anneal7 -minutes at 1500 F. AC A sheetbar of alloy containing 8% aluminum, 1% Ro11 15% reduction molybdenum,1% vanadium, balance tltanlurn havlng a a beta transus of 1900 F. i25was unidirectionally hot Anneal 7 minutes at 1500 F. AC

rolled from a temperature of 2100 F. to produce a hot Roll-45% reductionh fi h d hours at 14505 Rvcl band of 0.120 inch thickness. T e r0 mg n1se at 1650 F., and the ma or portlon thereof was carried out Roll 20%reduction Annea1 6 minutes at 16005 R Ac 1n the alpha-beta field as thebar cooled during rolling. A lvacuum c001 7 slower than air c001 parsiglflrq om the hot Sand) was heated for five mmlpteg at 19 and queue ed yimmersion in water. T e eta The cold rolled P5111e1 W21S free frominternal Cracking quench produced an acicular type microstructure in theand showed no ridging when a 3-inch by 10-inch test piece metaL Wasstfotohofl to an elongation of about ribbing The beta quenched panel wasthen subjected to cold was discernible at any stage after the betaquench. A rolling and annealing according to the following sequence:specimen of the finished cold rolled test piece was sec- R n 107 dtioned and polished and its microstructure found to be i He 2 F Vc 1equiaxed fine-grained and substantially completely re- 40 nnea ours?Roll15% reduction crystallized. A 1 7 t t F AC A second bar of thisalloy was unidirectionally hot g i g a rolled from a temperature in thebeta field to thickness A t F Ac of 0.135 inch. A plurality of panelswere cut from the hot g g 233;? a band, and each panel was heated at1950 F. for five gg i gi F Vcl minutes after which it was waterquenched. Following Rol1 15(7 reducfo the beta quench the panels weresandblasted and pickled Ann minute; F AC in order to clean the surfaceof the metal. The panels were then rolled at 1000 F. to efiectreductions of 15%, 20%, 1 Vacuum Slower than C001- 25% and 30% afterwhich each panel was further reduced The fi i h d o a panel was freefrom internal cracklng and 40% at 1000 F. A five mlnute anneal at 1650F. and showed no id i g when a 2-inch by 10-inch plece Was CQOImg bysandblasting n o o Was cold stretched to an elongation of about 6%. Noribbing 323.? $533??? l fiiifiity iiii ifii rs iiftl ii fiiii loil' If,dimmible final piodlflct w at uy stag. (1. .5. e processing 0 e pane ater t e eta quenc 25,531 fizz/ gli i ggi-rgg 2 1:22:3 g gg specimeln1trfdthe finished cold rolled panel was sectioned and p0 is e and itsmicrostructure found to be finer gno i k In 2 ih b t g obszrvod grainedand substantially completely recrystallized. mg q 0 o o a quono an 110Another bar of Ti-8Al-1Mo-1V alloy was unidirectiong g gzggg 3 :5 w geq-ah 511 hct T3116: from a itlemperalture in the beta field to o a 1115r 1S a ct an o 0.140 inc Pane s were cut from the hot for 0.070 inchgauge and below and 5.0 for strip thicker band and annealed at 1950 F.for five minutes followed than 0.070 inch. All speciments met thesespecifications. by quenching in water. Each beta quenched panel wasTABLE 0 Test E, 20 gauge Ftu, Fty, Percent p.s.i. MBR 1,000 F. cyclesinch Dir. Ks.i. Ks.i. E1 X R/T 15%,-40% .075 L 132.5 121.8 18.7 15.7 3.3T 133.5 123.9 18.5 17.0 2.5 20%-40% .071 L 133.6 120.4 19.0 10.0 3.5 T132.6 125.1 19. 5 18. 1 3. 5 25%-40% .055 L 134.5 121.2 18.5 15.8 3.8 T133.5 125.4 19.0 17.7 3.0 30%-40% .060 L 132.4 110.0 19.3 15.9 3.9 T130. 7 121. 5 18. 3 17. 3. 5

"One inch gauge.

9 10 then sandblasted and pickled and rolled at 1000 F. to TABLE Geffect a 30% reduction, annealed at 1650 F. for five minutes followed byair cooling rolled at 1000 F. to R m 20X F effect a 40% reduction,sandblasted and plckled and an teinpf F. Dir. Ksii K 53 1 Qla fg/ nealedfor forty-eight hours at 1450 F. followed by 5 1,400 L 1381 12% m7 16.9as vacuum cooling. The microstructure of the panels was T 132.5 127.520.5 13.1 3.7 fine grained and substantially completely recrystallizedL600 "g 13%? i 7.9 3.7 after the forty-eight hour anneal. Individualpanels were then cold rolled through one, two, three and four 20%gaugereduction cycles with a five minute anneal at 1650 F. EXAMPLE 1Vfollowed by an coolmg between each cycle. Subsequent to the last rollingcycle, each panel was annealed at 1450" A Panel of mmer ia ly Puretitanium, Ti-75A, was F. for forty-eight hours followed by vacuumcooling to cut from a unidirectionally hot rolled band having 3. effecta second recrystallization. Each of the panels was thickness of inchcontaining 0-3O4% Oxygen and successfully cold rolled without internalshear cracking. 15 havlng a beta tfanslls of 1725-1750 The Panel Was Ash wn i T bl E, th t l was du til d i cold rolled to 0.10 inch and washeated at a temperature tropy was low. No ribbing was observed duringrolling of 1800 F. for 2.5 minutes. The panel was then quenched andspecimens were elongated without ridging. The acy YaPId immersion in aCold Water bath- The beta quench ceptable bend radius for Ti-8Al-1Mo-1Vis 4.0 for 0.070 Produced all aciclllaf yp microstructure in e me alinchgauge and below and all samples tested met this The beta quenched Panelwas then Subjected to f0111' specification. cycles of 15% reduction atroom temperature usin TABLE E Test E, 20 gauge Ftu, Fty, Percent p.s.i.MBR Cold rolling inch Dir. Ks.i. KS1. El" 10 RI'I None .055 L 138.6129.5 20.0 16.9 3.7 T 134.5 127.5 22.0 17.9 2.9 One 20% cycle .044 L137.9 127.4 20.0 16.8 3.9 T 135.0 124.7 19.5 13.0 3.5 Two 20% cycles.033 L 134.6 122.0 19.5 16.7 3.7 T 129.0 120.4 21.0 17.7 3.1 Three 20%cycles .024 L 131.8 122.3 21.8 18.2 N.T. T 125.9 121.5 21.5 13.4 3.2Four 20% cycles .018 L 131.8 118.5 20.5 15.7 3.9 T 127.3 118.5 23.3 17.23.2

One inch gauge. N.T.-Tot tested. N

A pair of Ti-8Al-1Mo-1V alloy panels were treated 1400 F. seven minuteintermediate anneals. The final in the same way as the panels in theimmediately preanneal effected substantially complete recrystallization,ceding group except that after the first reduction 40 and the finishedcold rolled strip was free from internal at 1000 F. and the followinganneal, the panels were cracking and showed no n'dging when a 2-inch by10-inch rerolled at 1000 F. through two and three 30% reductest piecewas cold stretched to an elongation of about tion cycles at 1000 F. Eachrolling cycle was followed 10%. No ribbing was discernible either in thefinal by a five minute anneal at 1650 F. and air cooling, and product orat any stage after the beta quench. A specimen the last rolling cyclewas followed by sandblasting, pickof the finished cold rolled strip wassectioned and polling and a forty-eight hour recrystallization anneal at1450 F. and vacuum cooling. These panels also exhibited substantiallycomplete recrystallization and direc tionality was low as shown in TableF. No ribbing occurred during rolling and the panels were elongatedwithout ridging.

ished and its microstructure found to be recrystallized.

Six additional panels from the same 0.150 inch hot band were heated at1850 F. for five minutes and then rapidly cooled by immersion in water.The beta quenched panels were sandblasted and pickled and rolled a totalof at 600 F., 800 F., 1000 F., 1200 F., 1400 F.

*One inch gauge.

and 1600 F. respectively. The panels rolled at 1000 F. and below werecompletely recrystallized into equiaxed grains by a 1650 F. ten minuteanneal followed by air cooling. The tests performed on these panelsshowed no ridging, low anisotropy and high tensile and bend ductility asshown in Table H. All specimens met the bend specifications of 2.5 for0.060 inch and below and 3.0 for strip thicker than 0.060 inch. Thepanels rolled at 1200 F. and above recrystallized simultaneously withrolling. These panels demonstrated good mechanical properties and highductility without an anneal. A 1650 F. ten minute anneal followed by aircooling further 1 1 increased the ductility by completely stressrelieving the hot rolled structure.

12 60% at 1000 F. and annealed for ten minutes at 1650 F. followed byair cooling in an attempt to recrystalllze TABLE H Test 20X gauge, FtuFty Percent E, p.s.i. MB R Rolling temp., F. inch Dir. K at K s.i. El" X10 RT 054 L 97. 1 72. 8 31. 14. 9 2. 1 600 T 96. 2 80. 1 29. 0 17. 3 2.0 800 059 L 94. 2 66. 33. 0 15. 5 2. 0

'1 96. 1 80. 9 3 055 L 96. 4 73. 0 5. L000 T 93. 0 77. 5 2s. 5 16. a 2.1 1,200 055 L 96. 0 70. 4 32. 0 l5. 6 2. 1 T 104. 7 82. 0 29. 0 19. 5 2.1 1,400 054 L 97. 5 71. 4 33. 0 15. 7 2. 1 T 96. 9 78. 8 26. 5 17. 0 2.1 1,600 055 L 94. 6 64. 5 36. 0 l5. 1 2. 1 T 100. 0 81. 8 29. 0 17. 4 2.1

*One inch gauge.

The effect of the beta quench on the ribbing and ridging characteristicsof titanium alloy is clearly shown by the results of a test in which hotband panels of Ti-5Al-2.5Sn alloy were rolled at 1000 F. to effect a 60%reduction and box annealed at 1450 F. for forty-eight hours followed byvacuum cooling. One panel had been beta quenched prior to rolling andannealing and the second panel was rolled as received. Themicrostructures of both panels were recrystallized to the same extent.However, when the panel which was not beta quenched was pulled to 10%elongation, ridging occurred while no ridging took place in the betaquenched panel.

Panels of Ti-8Al-lMo-1V alloy and Ti-6Al-4V alloy were also cold rolledfrom non-beta quenched hot bands, and in each instance ridging occurredwhen the rolled panels were stretched at less than 10% elongation.

In order to ascertain the necessity of rapid cooling from the beta fieldto create the acicular type microstructure, comparative tests wereconducted. The tests and the results are set forth hereinafter.

Test A The test panels of Ti-8Al-1Mo-1V alloy were taken from aunidirectionally hot rolled hot band at 0.150 inch gauge and were heatedat a temperature of 1950 F. for five minutes. One of the panels waswater quenched below the beta transus, and the other was air cooled.Metallographic examination showed that the quenched panel had anacicular alpha structure, whereas the air cooled panel had a lamellaralpha structure. Both panels were then rolled at 1000 F. to effect a 30%reduction, annealed at 1650 F. for five minutes followed by air coolingand rolled again at 1000 F. to effect a 40% reduction. Both panels werethen box annealed at 1450 F. for forty-eight hours followed by vacuumcooling. Examination of the panels showed that the micro-structure ofthe air cooled panel was not completely recrystallized and still showedremnants of the beta heated structure while substantially completerecrystallization occurred in the quenched panel. In order to determinethe cold rollability of the metal, both panels were cold rolled throughthree cycles of reduction with a five minute line anneal at 1650 F. withair cooling after each reduction. Internal shear cracking occurred inthe air cooled panel during the first cold reduction, and the crackingincreased during the second and third reductions. No cracks occurred inthe panel subjected to the beta quench even after the third cycle of 15%reduction.

Test B Two panels of Ti-5Al-2.5Sn alloy were taken from a hot band at0.130 gauge and heated at 1950F. for five minutes. One of the panels wasair cooled to below the beta transus and the other was water quenched.Metallographic examination of the panels showed an acicular alphastructure in the quenched panel and a lamellar alpha structure in theair cooled panel. Both panels were then reduced the micro-structure. Themicrostructure of the air cooled panel was not completelyrecrystallized, whereas that of the quenched panel was. The panels werethen cold rolled through three cycles of 15%, 20% and 25% reductlon, andserious cracking occurred in the slowly cooled panel during the 15%reduction cycle and the cracking increased during the next two cycles.No cracking occurred in the panel subjected to the beta quench.

The results of tests A and B clearly show that cooling to a temperaturebelow the beta transus at a rate sufiiciently rapid to create anacicular alpha structure prevents internal shear cracking and isessential to obtain complete recrystallization.

As Will be appreciated by those skilled in the art, the degree ofreduction must be considered in conjunction with the rolling temperatureand the desired final gauge in order to produce recrystallized striphaving good ductility and minimum anisotropy. For example. Ti-8Al-1Mo-1V alloy can be recrystallized by two 20% reductions and a 30% reductionat 600 F. with intermediate five minute anueals at 1600 F. followed by afinal recrystallization anneal at 1450 F. for forty-eight hours or by asingle 60% reduction at 1200 F. followed by a 1450 F. anneal forforty-eight hours.

A temperature which has proved advantageous for rolling Ti-5Al-2.5Sn,Ti-6Al-4V and Ti-8Al-1Mo-1V alloys is 1000 F. The Ti-5Al-2.5Sn can bedirectly reduced 60% at this temperature without any intermediate stressrelief anneal as is shown in Example I. The Ti-6Al-4V and Ti- 8Al-lMo-1Valloys must be reduced in at least two cycles at 1000 F. with anintermediate partial stress relief anneal. The initial reduction forTi-6Al-4V may vary from about 15 to 35% and for Ti-SAl-lMo-IV from about20 to 35%. Initial reductions of these two alloys much in excess of 35%at 1000 F. will result in internal shear cracking, and reductions muchless than the above indicated minimum will impart insufficient strain tothe metal at this temperature to permit recrystallization. If only tworeduction cycles are used at 1000 F., the second reduction cycle forTi-6Al-4V and Ti-8Al-1'Mo-1V must be about 40% although it may beslightly lower depending upon the amount of reduction accomplishedduring the preceding reduction cycle. The degree of reduction necessaryin the second cycle is a function of the degree of reduction of thefirst cycle since a portion of the strain energy imparted to the metalduring the first cycle carries over and is added to the strain createdby the second cycle if the intermediate anneal is properly designed.Hence, a larger first reduction and a relatively low temperature shortduration anneal will permit recrystallization with less reduction in thesecond cycle since less strain energy will be required during the secondcycle. It is possible to utilize more than two reduction cycles ifdesired, and as many as five 30% reduction cycles with intermediateanneals have been used to produce quality strip. Since larger reductronsare required at the elevated temperatures to impart the necessary strainto the metal, it is important to beta quench the hot band directly withno preliminar rolling so that a recrystallized strip of reasonablethickness may be obtained for subsequent cold finishing.

After recrystallizing by rolling at elevated temperatures and annealing,the titanium strip alloys can be cold rolled without internally shearcracking up to 100% more than is possible by directly cold rolling betaquenched material. Subsequent to recrystallization they can also be coldrolled through several cycles of reduction with intermediate annealsdown to very thin gauge. The proper anneal after cold rolling willresult in a second complete recrystallization. For example, a fifteenminute anneal at 1650 F. will recrystallize Ti-5A1-2.S Sn alloy for thesecond time after it has been cold-rolled through one or more 20%reductions; and a forty-eight hour anneal at 1450 F. followed by vacuumcooling will recrystallize Ti-8A1-1Mo-1V and Ti-6A1-4V alloys for thesecond time after they have been cold rolled through one or more 2reductions.

Tests have shown that when rolling at room temperature and annealing areused to effect recrystallization, the maximum reduction possible percycle without internal shear cracking of the beta quenched hot band isabout 10 to 15% for the Ti-6A1-4V and Ti-8A1-1Mo-1V alloys and about 15to 20% for Ti-A1-2.5 Sn alloy. Heavier cold reductions than these afterthe beta quench cause internal shear cracking of the metal. However, itis possible to obtain a finished strip with a recrystallizedmicrostructure by effecting larger cold reductions prior to the betaquench and rolling to gauge in one or two cycles after the beta quenchdepending upon the alloy. As pointed out heretofore, it is not necessarythat the metal be beta quenched immediately after unidirectionally hotrolling to hot band so long as suflicient reduction is effected afterthe beta quench to impart strain to the metal so that substantiallycomplete recrystallization will occur during the final anneal. Thedesired finish gauge is, therefore, a determining factor in respect ofthe degree of reduction taken after the beta quench and the reductiontemperature, as the metal must be reduced by an amount sufiicient tocreate the required strain after the beta quench. The temperature ofrolling will determine the degree of reduction required to impart strainto the metal as less reduction is required at lower temperatures tocreate the strain necessary for subsequent recrystallization.

The recrystallization anneal provides the driving energy necessary torecrystallize the strained microstructures into v strain free equiaxedgrains; therefore, the exact temperatures and times used are dependenton the rolling cycles used. The recrystallization temperature selectedmust not be above the beta transus since the object is to recrystallizethe alpha structure and not transform alpha into beta. For alpha typetitanium alloys a relatively short time line anneal will result incomplete recrystallization. For example, a ten minute anneal at 1650 F.followed by air cooling is satisfactory for Ti-5Al-2.5 Sn. Much longeranneals are required for the alpha-beta type alloys and Ti-8Al-lMo-1Vand Ti-6A1-4V require fortyeight hour anneals at 1450 F. for effectingsubstantially complete recrystallization. The longer anneals are termedbox anneals and are performed on coils generally in a vacuum furnace toprevent contamination of the metal surface, although the use of a vacuumfurnace is not a requirement for our process. Temperatures for vacuumanneals are limited to about 1450 F. because at higher temperaturestitanium tends to stick together when under a vacuum; and such is, ofcourse, detrimental to coil annealing.

It should be understood that descaling and pickling of the strip is nota requirement of our process. Descaling and pickling clean the surfaceand reduce further contamination, and removal of oxides and scale priorto a rolling pass prevents enlarging and spreading these defects.

The method of our invention is advantageous in the production ofelongated strip titanium and certain titaniurn base alloys fromunidirectionally hot rolled hot band. The strip produced by our methodis completely free from ribbing, has no tendency toward ridging and hasminimum anisotropy. The beta quench and subsequent deformation andannealing provide equiaxed recrystallized grain structure, and thematerial can readily be finish cold rolled without internal cracking.Additionally, the material has good ductility and can, therefore, meetbend specifications.

While preferred embodiments of the invention have been described, it maybe otherwise embodied within the scope of the appended claims.

We claim:

1. A method for producing strip of a metal selected from the groupconsisting of commercially pure titanium, alpha stabilized alpha typetitanium base alloys and alpha stabilized alpha-beta type titanium basealloys, which cornprises:

(1) unidirectionally hot rolling a body of said metal to reduce saidbody to an elongated hot band, said rolling being initiated at atemperature requiring a substantial amount of said reduction to occur inthe alpha-beta field of said metal,

(2) heaing said hot band at a temperature above the beta transus of saidmetal to completely transform the crystal structure of said metal to thebeta phase,

(3) rapidly cooling said hot band from said temperature above the betatransus of said metal to a temperature below said beta transus toproduce an acicular type microstructure in the metal and (4) subjectingsaid rapidly cooled hot band to the steps of rolling and annealing attemperatures below said beta transus to produce an elongated striphaving a substantially completely recrystallized microstructure.

2. A method as set forth in claim 1 including rolling said hot bandprior to heating said hot band at a tem perature above said beta transusof said metal to effect a reduction in the thickness of said hot bandprior to said heating.

3. A method as set forth in claim 1 including stress relief annealingsaid rapidly cooled hot band at a temperature below the beta transus ofsaid metal prior to rolling said hot band.

4. A method as set forth in claim 1 wherein said unidirectional hotrolling of said body is initiated at a temperature above the betatransus of said metal.

5. A method as set forth in claim 1 wherein said unidirectional hotrolling of said body is initiated at a temperature sufi'iciently high inthe alpha-beta field of said metal that the beta phase of said metal isunstable.

6. A method as set forth in claim 1 wherein said heating of said hotband is at a temperature between the beta transus of said metal andabout F. above the beta transus of said metal.

7. A method as set forth in claim 1 wherein said heated hot band israpidly cooled from said temperature above the beta transus of saidmetal by immersion.

8. A method as set forth in claim 1 wherein said heated hot band israpidly cooled from said temperature above the beta transus of saidmetal to room temperature.

9. A method as set forth in claim 1 wherein said rolling of said rapidlycooled hot band is at a temperature between room temperature and about1600 F.

10. A method as set forth in claim 1 wherein said rolling of saidrapidly cooled hot band is at about 1000 F.

11. A method as set forth in claim 1 wherein said rolling of saidrapidly cooled hot band consists of a plurality of rolling cyclesbetween room temperature and about 300 F. and wherein said annealingconsists of an anneal after each rolling cycle.

12. A method as set forth in claim 11 including rolling said hot handbetween room temperature and about 300 F. to effect a substantialreduction prior to heating 15 said hot band at a temperature above thebeta transus of said metal.

13. A method as set forth in claim 1 wherein said metal is an alloyconsisting essentially of 5% aluminum, 2.5% tin, balance titanium, andwherein said rolling of said rapidly cooled hot band consists of aplurality of cycles at room temperature with a maximum reduction of 15%to 20% in each cycle and said annealing consists of heating at about1600" F. for about five minutes after each rolling cycle whereby thefinal anneal produces said substantially completely recrystallizedmicrostructure in said elongated strip.

14. A method as set forth in claim 1 wherein said metal is an alloyconsisting essentially of 5% aluminum, 2.5% tin, balance titanium, andwherein said rolling of said rapidly cooled hot band consists of asingle cycle at about 1000 F. to effect a reduction of about 60% andsaid annealing consists of heating at about 1650 F. for about tenminutes to produce said substantially completely recrystallizedmicrostructure in said elongated strip.

15. A method as set forth in claim 1 wherein said metal is an alloyconsisting essentially of 8% aluminum, 1% molybdenum, 1% vanadium,balance titanium, and wherein said rolling of said rapidly cooled hotband consists of a plurality of cycles at room temperature with amaximum reduction of 10% to in each cycle and said annealing consists ofheating after each rolling cycle, the final heating being at about 1450F. for about fortyeight hours to produce said substantially completelyrecrystallized microstructure in said elongated strip.

16. A method as set forth in claim 1 wherein said metal is an alloyconsisting essentially of 8% aluminum, 1% vanadium, balance titanium,and wherein said rolling of said rapidly cooled hot band consists of aplurality of cycles at about 1000 F. with a reduction of to 35% in eachcycle and said annealing consists of heating at about 1650 F. for abovefive minutes between rolling cycles and heating at about 1450 F. forabout fortyeight hours after the final rolling cycle to produce saidsubstantially recrystallized microstructure in said elongated strip.

17. A method as set forth in claim 1 wherein said metal is an alloyconsisting essentially of 8% aluminum, 1% molybdenum, 1% vanadium,balance titanium, and wherein said rolling of said rapidly cooled hotband consists of a first cycle at about 1000 F. to effect a reduction ofabout and a second cycle at about 1000 F. to effect a further reductionof about 40% and said annealing consists of heating at about 1650 F. forabove five minutes after said first cycle and heating at about 1450 F.for about forty-eight hours after said second cycle to produce saidsubstantially completely recrystallized microstructure in said elongatedstrip.

18. A method as set forth in claim 1 wherein said metal is an alloyconsisting essentially of 6% aluminum, 4% vanadium, balance titanium,and wherein said rolling of said rapidly cooled hot band consists of aplurality of cycles at room temperature to effect a maximum reduction of10% to 15% in each cycle and said annealing consists of heating aftereach rolling cycle, the final heating being at about 1450 F. for aboutforty-eight hours to produce said substantially completelyrecrystallized microstructure in said elongated strip.

19. A method as set forth in claim 1 wherein said metal is an alloyconsisting essentially of 6% aluminum, 4% vanadium, balance titanium,and wherein said rolling of said rapidly cooled hot band consists of aplurality of cycles at about 1000 F. to effect a reduction of 15 to ineach cycle and said annealing consists of heating at about 1650 F. forfive minutes between rolling cycles and heating at about 1450 fQ aboutfo y g h urs after the final rolling cycle to produce said substantiallycompletely recrystallized microstructure in said elongated strip.

20. A method as set forth in claim 1 wherein said metal is an alloyconsisting essentially of 6% aluminum, 4% vanadium, balance titanium,and wherein said rolling of said rapidly cooled hot band consists of afirst cycle at about 1000 F. to effect a reduction of about 25% and asecond cycle at about 1000 F. to effect a reduction of about 40% andsaid annealing consists of heating at about l650 F. for about fiveminutes after said first cycle and heating at about 1450 F. for aboutforty-eight hours after said second cycle to produce said substantiallycompletely recrystallized microstructure in said elongated strip.

21. A method as set forth in claim 1 wherein said metal is commerciallypure titanium, and wherein said rolling of said rapidly cooled hot bandconsists of a plurality of cycles at room temperature with a reductionof 15% in each cycle and said annealing consists of heating at about1400 F. for about seven minutes after each rolling cycle whereby thefinal anneal produces said substantially completely recrystallizedmicrostructure in said elongated strip.

22. A method as set forth in claim 1 wherein said metal is commerciallypure titanium, and wherein said rolling of said rap-idly cooled hot bandconsists of a single cycle at about 1000 F. to effect a reduction ofabout 60% and said annealing consists of heating at about 1650 F. forabout ten minutes to produce said substantially completelyrecrystallized microstructure in said elongated strip.

23. A method for producing strip of a metal selected from the groupconsisting of commercially pure titanium and a titanium alloy consistingessentially of 5% aluminum, 2.5% tin, balance titanium, which comprises:

(1) unidirectionally hot rolling a body of said metal to reduce saidbody to an elongated hot band, said rolling being initiated at atemperature requiring a substantial amount of said reduction to occur inthe alpha-beta field of said metal,

(2) heating said hot band at a temperature above the beta transus ofsaid metal to completely transform the crystal structure of said metalto the beta phase,

(3) rapidly cooling said hot band from said temperature above the betatransus of said metal to a temperature below said beta transus toproduce an acicular type microstructure in the metal and (4) rollingsaid rapidly cooled hot band at a temperature below the beta transus ofsaid metal and sufficiently high to cause recrystallization of themicrostructure during said rolling, whereby said rolling produces anelongated strip having a substantially completely recrystallizedmicrostructure.

24. A method as set forth in claim 23 wherein said metal is an alloyconsisting essentially of 5% aluminum, 2.5 tin, balance titanium, andwherein said rolling of said rapidly cooled hot band is at a temperaturebetween about 1200 F. and 1400 F.

25. A method as set forth in claim 23 wherein said metal is commerciallypure titanium, and wherein said rolling of said rapidly cooled hot bandis at a temperature between about 1000 F. and 1200 F.

References Cited UNITED STATES PATENTS 7/1968 Parris 148-ll.5 2/1965Newman 148-115 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No 3 ,492 ,172 January 27 1970 Adrian Burt Sauvageot et al It iscertified that error appears in the above identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3 line 51 "heat" should read near Column 5, line 40, "rollingannealing" should read rolling and annealing Column 9 at the bottom ofTable E, "Tot tested." should read Not tested. Column 11 in the lastheading in Table H, "RT" should read R/T same column ll line 41 "The"should read Two Column 14', line 25 "heaing" should read heating Column15 line 32 molybdenum,"

should be inserted after 'aluminum,".

Signed and sealed this 23rd day of June 1970.

(SEAL) Attest:

EDWARD M.FLE CHER, JR. WILLIAM E. SCHUYLER, JR. Attesting Of icerCommissioner of Patents

